The present invention relates to a process for producing metals (which term includes metal alloys), in particular although by no means exclusively iron, from a metalliferous feed material, such as ores, partly reduced ores and metal-containing waste streams, in a metallurgical vessel containing a molten bath.
The present invention relates particularly to a molten metal bath-based direct smelting process for producing molten metal from a metallurgical feed material.
A known direct smelting process, which relies on a molten metal layer as a reaction medium, and is generally referred to as the HIsmelt process, is described in International application PCT/AU96/00197 (WO 96/31627) in the name of the applicant.
The HIsmelt process as described in the International application comprises:
(a) forming a bath of molten iron and slag in a vessel;
(b) injecting into the bath:
(i) a metalliferous feed material, typically metal oxides; and
(ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and
(c) smelting metalliferous feed material to metal in the metal layer.
The term xe2x80x9csmeltingxe2x80x9d is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce liquid metal.
The HIsmelt process also comprises post-combusting reaction gases, such as CO and H2, released from the bath in the space above the bath with oxygen-containing gas and transferring the heat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.
The HIsmelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
The applicant has carried out extensive pilot plant work on the HIsmelt process and has made a series of significant findings in relation to the process.
One significant finding is that it is possible to achieve a surprisingly high degree of control over the process by:
(a) injecting solid materials, such as metalliferous feed material and solid carbonaceous material, into the metal layer via a plurality of lances/tuyeres positioned above and extending towards the metal layer; and
(b) forming a pipe of a solid material, which typically is at least predominantly slag, on the ends of each lance/tuyere and thereby extending the lengths of the lances/tuyeres.
The control is the result of the lengths of the pipes automatically varying with the level of the molten metal and thereby maintaining a substantially constant spacing between the effective ends of the lances/tuyeres and the metal.
The length of a pipe on a lance/tuyere is determined by the level of molten metal in the molten bath in the vicinity of the lance/tuyere. Specifically, as the molten metal level increases there is a greater likelihood that molten metal that splashes or is otherwise projected from the metal layer will contact and melt the end of a pipe due to the higher heat transfer of metal compared with slag. In addition, as the molten metal level decreases there is less likelihood of contact of molten metal and the pipe and therefore the end of the pipe can progressively increase towards the metal layer. Variations in the molten metal level occur in continuous and batch metal tapping processes and thus the invention is relevant to both types of processes.
In addition to providing a high degree of control over injection of solid materials into the metal layerxe2x80x94which is important in a metal-based direct smelting process such as the HIsmelt processxe2x80x94the present invention makes it possible to operate with fixed solid material injection lances/tuyeres. This is an advantage because movable lances/tuyeres require seals and seals tend to be difficult to design for no leakage or failure.
In addition to the above advantages, the present invention makes it possible to position a lance/tuyere well clear of the splash zone of the molten metal and thereby avoid damage to the lance/tuyere by contact with molten metal, while ensuring that the effective end of the lance/tuyere is as close as possible to the metal layer. This makes it possible to use a water-cooled lance/tuyere without having the lance/tuyere too close to the molten metal to be a serious safety risk. This is a particularly important issue in a molten layer-based smelting process, such as the HIsmelt process. Thus, the present invention makes it possible to reconcile the conflicting requirements of (i) safety, which dictates positioning the lances/tuyeres as far aware as possible from the metal layer and (ii) performance, which dictates positioning the lances/tuyeres close to the metal layer to optimise injection of reactants into the metal layer.
According to the present invention there is provided a direct smelting process for producing metal from a metalliferous feed material which includes the steps of:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in a metallurgical vessel;
(b) injecting a carrier gas, a metalliferous feed material, and a solid carbonaceous material into the metal layer via a plurality of solid material injection lances/tuyeres positioned above and extending towards the surface of the metal layer and causing molten material to be projected from the molten bath as splashes, droplets and streams into a space above a nominal quiescent surface of the molten bath to form a transition zone;
(c) smelting metalliferous feed material to metal in the metal layer;
(d) injecting an oxygen-containing gas into the vessel via one or more than one lance/tuyere and post-combusting reaction gases released from the molten bath, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath, and whereby the transition zone minimises heat loss from the vessel via the side walls in contact with the transition zone; and
the process being characterised by forming a pipe of a solid material on the end of at least one lance/tuyere while injecting the metalliferous feed material and the carbonaceous material through the solid material injection lances/tuyeres and thereby extending the effective length of the lance/tuyere or the lances/tuyeres.
Typically, molten metal is a major part and slag is the remaining part of the molten material in the splashes, droplets, and streams of molten material from the metal layer. Typically, the splashes, droplets, and streams of molten material entrain further molten material (particularly slag) as they move upwardly. In addition, increasingly, the splashes, droplets, and streams of molten material lose momentum and fall downwardly towards the metal layer. In view of the higher density of metal than slag the relative amount of metal in the molten material in the splashes, droplets, and streams decreases with distance from the metal layer to the point where the transition zone may include small amounts, if any, metal.
The term xe2x80x9cmetal layerxe2x80x9d is understood herein to mean that region of the bath that is predominantly metal. Specifically, the term covers a region or zone that includes a dispersion of molten slag in a metal continuous volume.
The term xe2x80x9cslag layerxe2x80x9d is understood herein to mean that region of the bath that is predominantly slag. Specifically, the term covers a region or zone that includes a dispersion of molten metal in a slag continuous volume.
The space above the nominal quiescent surface of the bath is hereinafter referred to as the xe2x80x9ctop spacexe2x80x9d.
The term xe2x80x9cquiescent surfacexe2x80x9d in the context of the molten bath is understood to mean the surface of the molten bath under process conditions in which there is no gas/solids injection and therefore no bath agitation.
Similarly, the term xe2x80x9cquiescent surfacexe2x80x9d in the context of the metal layer is understood to mean the surface of the metal layer under process conditions in which there is no gas/solids injection and therefore no bath agitation.
Typically, the pipe or pipes are formed at least predominantly from solidified slag. The or each pipe may include some solidified metal.
Preferably the process includes locating each solid material injection lance/tuyere so that the outlet end is below the surface of the molten bath and above the metal layer.
Preferably the process includes locating each solid material injection lance/tuyere so that the outlet end is at least 150 mm above a quiescent surface of the metal layer.
Preferably the process locating each solid material injection lance/tuyere so that the outlet end is no more than 500 mm, more preferably no more than 400 mm, above a quiescent surface the metal layer.
In the context of the heights of the solid material injection lances/tuyeres above the quiescent surface of the metal layer described in the preceding two paragraphs, depending on parameters such as mass flow rate of solid material through the lances/tuyeres, the applicant found in pilot plant work that the length of the pipe or pipes was up to 600 mm, typically at least 200 mm. It can readily be appreciated that a pipe length of 600 mm, and a lance/tuyere angle of 30-60xc2x0 to the vertical, inevitably means that the pipe or pipes can extend below the quiescent surface of the metal layer. This is an important finding for a process which smelts at least predominantly in the metal layer because it means that there is significant penetration of solid material in the metal layer.
Preferably step (d) includes forming the pipe or pipes by injecting the metalliferous feed material and the carbonaceous material through the solid material injection lances/tuyeres so that the endothermic nature of these materials creates a region around the ends of the solid material injection lances/tuyeres which is below a temperature at which slag freezes. One important control parameter in this regard is to inject the metalliferous material and the carbonaceous material with an oxygen-deficient gas.
Accordingly, preferably step (b) includes injecting the metalliferous feed material and the carbonaceous material with an oxygen-deficient gas.
Preferably the process includes injecting the metalliferous material and/or the carbonaceous material so that the or each pipe forms as a co-axial extension of the or each solid material injection lance/tuyere. Important control parameters in this regard are the mass flow rate of the metalliferous feed material and the carbonaceous material and the velocity of the stream of the carrier gas, metalliferous feed material and the carrier gas.
Preferably the process includes maintaining the outlet end of each solid material injection lance/tuyere at a temperature below that at which slag freezes so as to encourage initial solidification of solid material on the ends.
More preferably the outlet end of each solid material injection lance/tuyere is water-cooled and the water cooling maintains the end at a temperature below that at which slag freezes.
Preferably the process is as described in International application PCT/AU99/00538 entitled xe2x80x9cDirect Smelting Processxe2x80x9d in the name of the applicant and the disclosure in that application is incorporated herein by cross-reference.
According to the present invention there is provided a vessel for producing metal from a metalliferous feed material by a direct smelting process, which vessel contains a molten bath having a metal layer and a slag layer on the metal layer, which vessel includes:
(a) a hearth formed of refractory material having a base and sides in contact with the molten metal;
(b) side walls which extend upwardly from the sides of the hearth and are in contact with the slag layer;
(c) one or more than one lance/tuyere extending downwardly into the vessel and injecting an oxygen-containing gas into the vessel;
(d) a plurality of solid material injection lances/tuyeres extending downwardly and inwardly into the vessel and injecting a carrier gas, a metalliferous feed material, and a carbonaceous material into the metal layer, an outlet end of at least one lance/tuyere being positioned above the surface of the metal layer during operation of the direct smelting process in the vessel and having solidified thereon a pipe of a solid material which forms an extension of the outlet end of the lance/tuyere; and
(d) a means for discharging molten metal and slag from the vessel.
Preferably the smelt reduction vessel is as described in International application PCT/AU99/00537 entitled xe2x80x9cDirect Smelting Vesselxe2x80x9d in the name of the applicant and the disclosure in that application is incorporated herein by cross-reference.
Preferably each solid material injection lance/tuyere is located so that the outlet end is below the surface of the molten bath.
Preferably each solid material injection lance/tuyere is located so that the outlet end is at least 150 mm above a quiescent surface of the metal layer.
Preferably each solid material injection lance/tuyere is located so that the outlet end is no more than 500mm, more preferably no more than 400mm, above a quiescent surface of the metal layer.
Preferably the pipe or pipes are at least 200mm, more preferably at least 300mm, at different stages of the process.
Preferably each solid material injection lance/tuyere includes:
(a) a hollow elongate member that defines a central passageway for the feed material and has an inlet end and the outlet end; and
(b) an outer water cooling jacket.
Preferably the member extends beyond the water cooling jacket at the outlet end of the lance/tuyere.
Preferably the outer surface of the water cooled jacket includes a dimpled or other surface profile that increases the exposed area of the water cooling jacket.
Preferably the solid material injection lances/tuyeres extend downwardly and inwardly into the vessel at an angle of 30-60xc2x0 to the vertical.
Preferably the outlet end of each solid material injection lance/tuyere is located in the slag layer.